An example of a portable radio communication terminal having both of the portable telephone function and the wireless LAN (Local Area Network) function is disclosed in patent document 1. The portable radio communication terminal of patent document 1 has a means which selects either the portable telephone function or the wireless LAN function, and download and upload of personal information is performed via either a cellular phone base station or a wireless LAN base station. In patent document 1, a composition that the user sets a line to use in advance, and, a configuration of measuring a throughput when connecting to each line and a terminal automatically selects a line with good communication environment are disclosed.
Further, an example of a communication terminal apparatus having a local proxy is disclosed in patent document 2. The communication terminal apparatus disclosed in patent document 2, together with having a plurality of interfaces, for example, a cellular phone interface, a wireless LAN interface, and a wired LAN interface, has a local proxy which operates at a TCP (Transmission Control Protocol) layer. To the local proxy, an IP (Internet Protocol) address of each interface is assigned. Further, the local proxy establishes a link with two of these interfaces, and monitors. Further, the local proxy selects and connects with one of interface, temporarily storing in a memory, and relays downloading of applications such as a browser. Then, when the failure of a link in the selected interface is confirmed, the local proxy selects other interface and continues the process. That is, in patent document 2, a communication terminal apparatus in which, by using the local proxy, a cellular phone and LAN interface are switched while continuing the process between the browser and the local proxy and a plurality of links such as a cellular phone are switched seamlessly, is disclosed.
Further, a data communication system in which a mobile equipment which performs wireless communication by switching a plurality of communication systems receives data transmitted from a providing server, is disclosed in patent document 3. The data communication system disclosed in patent document 3, according to the radio wave intensity of each communication system and the order of priority, selects a communication system for use. The mobile equipment is used by the user of an external terminal. The mobile equipment and the external terminal, for example, can be connected by using near field communication such as Bluetooth (registered trademark) and infrared data communication. The mobile equipment, according to the instruction from an external terminal, establishes communication with a content server by the selected communication system, and transmits and receives two-way data. In the data communication system disclosed in patent document 3, when the download of contents is completed, end of communication is indicated to the mobile equipment from an external terminal, and the mobile equipment transmits an instruction for communication termination to a common authentication server. The common authentication server which received the instruction for communication termination, replies the acknowledgement response to the mobile equipment. Further, patent document 3 discloses that the acknowledgement response is acquired from the mobile equipment by an external terminal.